It is generally known for scans to be carried out using relatively complex recording techniques, for example using contrast agent or using different X-ray energies, before computed-tomography-based interventions, in order to better identify structures which are difficult to identify, such as lesions in soft tissue parts. During the subsequent intervention, current computed-tomography imaging is then carried out in circumstances in which the load is reduced, since this examination in its own right generally produces a high dose because of the relatively long duration, with important additional information such as differences between soft parts being lacking in these circumstances.
Particularly when examining organs, for example a liver, it is particular difficult to distinguish between organ tissue, tumor tissue and vessels, so that complex examination methods which may result in a high patient dose, specifically the additional giving of contrast agents or the use of different spectra for the CT scan or else the use of a higher dose in order to improve the imaging, are used. Computed-tomography displays are then created using methods with lower doses during the subsequently carried out intervention, in which displays, for example, an originally identified tumor cannot be seen.
The problem is now to also obtain three-dimensional information about the position and size of a lesion during the planning examinations that are carried out first of all, and this information must be transferred to the displays during the actual intervention. Until now, this has been done by the user defining the position and orientation of a region of interest (ROI), that is to say of lesions, tumor tissues or regions which must not be injured, such as blood vessels, possibly with the assistance of landmarks, with these being transferred in an imaginary form to the scans during actual intervention on the basis of memory or, in an improved variant, by actual image comparison. On the one hand, this can lead to serious errors while on the other hand it places additional load on the user and represents a distraction from his actual task during the intervention.
It is also known for a previous image from the planning examination to be superimposed as a translucent image on the current scan and, if appropriate, to be shifted to produce as good a match as possible with the current scan during the intervention in order that the position of the ROI can be transferred as well as possible. When using a method such as this, one problem is that the entire scan has the planning examination scan superimposed on it, resulting in the current imaging process being in the background, as a result of which any changes in the current scan are overlooked.